Our objective is to measure, as indicators of colonic anaerobic microflora metabolism, breath methane and hydrogen and urine indoxyl and skatoxyl in: 1) 150 patients with colorectal cancer; 2) 150 patients with colorectal adenomas; 3) 80 members of "cancer families"; and 4) 100 age and sex matched controls. Fasting end-expiratory breath samples will be collected. Then oral lactulose will be given and four hourly breath samples collected. Breath methane and hydrogen will be measured using gas chromatography. Before lactulose administration 24 hour urine specimens will be collected and treated with B-glucuronidase/arylsulfatase. Urine indoxyl and skatoxyl will be extracted with methylene chloride and measured using gas chromatography. To study the effect of intraluminal bleeding on colonic microflora metabolism, 30 controls will receive bovine hemoglobin by mouth for seven days. Daily breath and urine specimens will be analyzed as indicated above. The strength of this approach is that it utilizes indirect non-invasive techniques to study metabolites produced exclusively by the anaerobic colonic microflora in subjects already known to have or to be at increased risk for developing colorectal cancer. This method, less expensive than current diagnostic techniques, is potentially applicable to population screening in order to select a subpopulation that might be at greater risk for developing colorectal cancer.